1. Field of the Invention
The present invention relates to a communication apparatus and a method of transferring data.
2. Description of the Related Art
Specifications of access control for improvement of Quality of Service (QoS) are developed for wireless local area network (LAN) systems in the related art (for example, Institute of Electrical and Electronic Engineers (IEEE) 802.11e Standard Medium Access Control Quality of Service Enhancements).
US Patent Publication No. 2002/0159418 (Japanese Patent Laid-Open No. 2002-314546) discloses the QoS in the IEEE 802.11e Standard. US Patent Publication No. 2005/0195858 (Japanese Patent Laid-Open No. 2005-252897) and US Patent Publication No. 2007/0032198 (Japanese Patent Laid-Open No. 2004-336730) propose methods of transmitting Media Access Control (MAC) frames in order to improve the throughput.
Block Ack scheme is defined in the IEEE 802.11e Standard. In a MAC frame transfer method in the related art, a receiver device transmits an acknowledgement (Ack) if the receiver device normally receives a MAC frame. The receiver device transmits a negative acknowledgement (Nack) if the received MAC frame is not normal because of any error or if no MAC frame is received within a predetermined time.
A transmitter device moves to a transmission process of the next MAC frame if the transmitter device receives an Ack and performs a retransmission process if the transmitter device receives a Nack. If the transmitter device does not succeed in the transmission even after the retransmission process has been performed a predetermined number of times, the transmitter device gives up the retransmission. The transmitter device then indicates to an upper layer that the transmission abnormally terminates and performs the retransmission process at the upper layer. There are cases in which the receiver device does not return a Nack or in which the transmitter device cannot receive a Nack for any reason. In such cases, the transmitter device performs the retransmission process if the transmitter device receives no Ack within a predetermined time.
If a MAC frame is damaged or any error, such as transmission delay, occurs on the transmission path when media data, such as a motion picture, is transmitted in a system performing the MAC frame transfer method, the retransmission process is performed in a MAC level. However, the receiver device cannot display data concerning the motion picture that is received unless it receives the data within a predetermined time. Accordingly, there are cases in which the receiver device cannot use the data even if the retransmission process is performed, thus offering the inefficient retransmission method.